Embodiments of such presses with an upper drive and a bottom drive for the plunger have previously been described. For example, the respective element of the drive train connected to and driving the plunger can be designed as a tie rod/connecting rod in a bottom drive or as a threaded spindle in an upper drive or as an element, which directly generates a force such as a piston/cylinder unit.
In presses with a bottom drive, for example, the plunger can thus be driven by a compact drive unit in a sub-structure of the press by way of tie rods—also in conjunction with a connecting rod—or by way of threaded spindles serving as traction elements.
Irrespective of the type of the drive, a tilting of the plunger may occur due to eccentric forces acting during the machining process. Providing a parallel run of the plunger to the sub-structure is, however, often required.
To date, various solutions, which are substantially implemented by appropriate expenses for the drive the plunger or by different embodiments of the plunger guide, are used to achieve a required parallel operation.
It has proven disadvantageous, for example, that a complex but softly reacting kinematic lever system described in AT 215 257 B is inefficient for transmitting eccentric forces. When strong pressing forces are to be transmitted, the relatively numerous mobile machine elements generate only small compensatory movements for an efficient plunger stroke.
Presses (with an upper drive as well as with a bottom drive) must, however, be designed so that they can provide an optimized force and path progression of the plunger and its stroke and can act in a differentiated manner according to machining requirements. Positions of individual machine elements and of the plunger which deviate from normal positions must be absorbed and compensated for as much as possible by the structural system with regard to forces in order to avoid complex embodiments of the plunger guide on the one hand and to provide the machining process on the other hand.
It has already been proposed to record values about operating conditions in the system of the press during machining of the workpiece by means of a control and regulation device and to process them into data according to a function, so that the data is also usable to a limited extent for compensatory movements of the plunger. The press can thus be operated in a controlled or regulated manner according to a system of forces required for machining the workpiece.
In generic presses, the drawing process, e.g., by means of so-called drawing devices and drawing cushions, also has a decisive impact on the positions of the plunger with regard to its horizontal position.
In a punch press described in EP 2 008 799 A1 with a bottom drive, the plunger was driven by way of tie columns (similar to tie rods) by means of a drive mechanism with a crankshaft and connecting rod disposed below the machining level. Bearing loads are here to be reduced by means of a special transmission mechanism and a distribution of the plunger forces and a high precision is to be achieved at high frequencies. Positions of the plunger deviating from the horizontal are not, however, compensable.
With regard to current requirements for presses, wanted or unwanted compensatory movements occurring during the process must be possible. This aims at fulfilling the conditions for a practical operation in order to achieve a synchronous operation or compensatory movements of the plunger during at least a partial segment of its strokes.
In presses with a bottom drive, this thus also applies to the area of the articulation points of the tie rods to the plunger which are often designed as detachable, fixed connections to the plunger.
WO 2012/041313 described, in spite of occurring asymmetrical forces, such as e.g., in a drawing device, securing a guide so as to cause an originally desired movement of the plunger as well as movements of the upper tool part parallel to the bottom tool part, by way of separately operated drive trains having tie rods which independently apply forces to the plunger. Thus, on the one hand, a tilting of the plunger as well as various impacts of the plunger can be avoided and, on the other hand, the tilting of the plunger can be induced in a targeted manner.
It has thus already been proposed to use asymmetrically acting forces of the plunger in an advantageous manner and letting the plunger impact e.g., the drawing cushion device in parallel or, in the absence of a drawing cushion device, to drive the plunger with the upper tool part in parallel so that it bears down onto the bottom tool part. To this end, the e.g., two drive trains must be moved by different distances in the direction of the bottom dead center but without reaching it. A reversal (inversion of the rotational direction of the drive) and an upward movement of the plunger subsequently occur.
As an alternative, one drive train can even move through the bottom dead center and be moved back to the top dead center without a reversal, whereas the other drive train moves back to the top dead center before reaching the bottom dead center by way of a reversal. The respective position of the respective drive train is then decisive for generating the actually acting force.
DE 196 42 587 A1 described a multi-point press with hydraulic pressure pads and inversely adjustable spring stiffnesses of the pressure points for compensating for the tilting of the plunger in order to achieve a parallel positioning of the plunger in presses, which fulfills requirements such as:                reaction to eccentric loads without delay;        precise operation;        strong reliability; and        simple, cost-effective structure.        
Process disruptions resulting from a tilt of the table relative to the plunger or from eccentric loads on the plunger are therefore to be avoided in mechanically driven multi-point presses with eccentrically running work processes.
An aspect of the present invention is to compensate for the tilting of the plunger so that a plunger movement that is exactly parallel to the press table is for the most part provided.
Therefore, the principle of a solution includes:                a parallel positioning of the plunger in multi-point presses with hydraulic pressure pads, wherein the spring stiffnesses in the pressure points is modified so that different longitudinal deformations of the frame and connecting rod caused by eccentric loads are compensated for by a reduction of the stiffness of the associated pressure pad(s),        to this end, the spring stiffness of the pressure points of the press is adjusted so that the total spring stiffnesses of the pressure points, obtained by adding up the spring stiffnesses of the individual pressure pads of the press and the spring stiffnesses of the associated elastically deformed machine parts, and the forces to be transferred by the individual pressure points of the press behave in inverse proportion relative to each other and        the less loaded pressure pad(s) is connected to a pressure accumulator, more specifically, a piston accumulator and the preload pressure of the pressure accumulator, more specifically, the gas pressure of the piston accumulator, is adjusted according to the desired reduction of the stiffness of the associated pressure pad.        
The problem “tilting of the plunger vs. parallel positioning of the plunger” is only seemingly solved by this synopsis of solutions according to this stage of development.
DE 10 2005 040 263 A1 described the problem of developing a method and a device for controlling and regulating the movement of the plunger in servo-electric presses in order to achieve a precise and repeatable sequence of the movement of the plunger in phases of a position-controlled as well as in phases of a force-controlled movement of the plunger. A controlled operation was meant to provide a high output between several plunger pressure points of one plunger as well as of several plungers of a press line, respectively, relative to each other and relative to peripheral devices.
The control accuracy of the tilt control in highly dynamic processes, usable in case of eccentric forces, of a plunger equipped with several pressure points was also meant to be improved.
In order to regulate the movement of the plunger, the central idea was to combine the principle of a main-shaft-controlled electronic cam disc adjustment with the force adjustment so that, depending on the operation mode, the phases of the movement of the plunger are controlled via electronic position cam discs and via a force adjustment or force limitation.
In addition to a compensation of the variable resiliency of all the drive elements located in the force flow occurring in case of an eccentric load, a tilt control of the individual pressure points was also meant to use the generation of a nominal tilt of the plunger, however, this position control occurred by means of the position cam disc and of a position offset.
From this teaching, the person skilled in the art could indeed gather, on the one hand, the idea of using all the drive elements located in the force flow for compensating the different resiliencies occurring under eccentric loads and, on the other hand, the idea of generating a nominal tilt of the plunger, but always provided that the nominal torques of the servomotors for driving the pressure point(s) of the plunger would be controlled as a function of influencing values such as gear ratio and/or resiliency by means of position cam discs controlled by a virtual main shaft and a force and moment limit value dependent on the operation mode.
Continuing this development, DE 10 2006 059 796 A1 describes a method and a device for controlling and regulating the drive system of a press in which the reproducibility of the quality of the formed parts to be produced is improved in spite of the effects of disruptive influencing values, the service life of the tools is increased, and the productivity is increased while simultaneously reducing the energy consumption.
To this end, the tilt of the plunger is controlled by a preset, servo-driven, position-adjusting device, separately associated with each pressure point. The person skilled in the art already recognized that the asymmetrical spring travels had to be determined by way of the eccentric load specific to each part while taking into account the stiffness model specific to the machine.
The actual compensation of the plunger tilt occurs, however, by way of a relatively complex target/actual comparison of the pre-set asymmetrical adjustment of the position of the plunger and the asymmetrical motion sequence of the servomotors for the main drive additionally associated with the pressure points.
During the 360° cycle mode, an tilting of the plunger at the top dead center is to be avoided according to a second embodiment by respectively traveling through the area of the top dead center in the cycle with a symmetrical adjustment of the position, the asymmetrical position adjustment being reactivated after the top dead center before the subsequent load phase.
In a third embodiment, the regulation of the tilt of the plunger is meant to take place so that during the load phase in the area in front of the bottom dead center, the position of the plunger or upper tool with regard to the tilting and deviation of the bottom dead center is recorded by means of a plunger position measuring device and the tilted position and, if necessary, the immersion depth is influenced in a control circuit.
According to a fourth embodiment, the immersion depth of the plunger is to be controlled. The expected variations of the reversal position of the plunger or tool are here stored in the control unit as a function of influencing values such as temperature changes and stroke rates conditioned by the operating time, while taking into account a model specific to the machine.
The central idea of these solutions is to influence, in a servo-electric forming press, the positional deviations of a plunger, drivable by means of a crank or a lever, caused by external and internal influencing values in a stroke-dependent operating mode when passing through the bottom dead center so that the immersion depth and the tilted position of the plunger is controllable or adjustable. However, using the cam disc regulation to control the servomotors for the main drive, which require separate electronic cam discs for each drive associated with each pressure point, is common to all four embodiments.
The person skilled in the art can see that the behavior of these presses is influenced in relation to a pre-set virtual main shaft, wherein the deviation of the individual servomotors from the pre-set main shaft position is to be influenced. This requires various preparation phases, which require a complex sequence for achieving a corresponding setting of the machine.
In view of these analyses, the problem of allowing the asymmetrically occurring press forces as well as drawing cushion forces to cause an unwanted tilting of the plunger such as caused by a malfunction or of counteracting it or of initiating a desired tilting of the plunger with simpler means such as available structural components, i.e., providing a desired parallel movement of the plunger by means of controlled and regulated drive motors, still remains.
A further development aiming at associating a cam disc regulation, with separate electronic cam discs for each drive, to the main drive is therefore ruled out.
The objective impact of Hooke's law in the constructional system of a press, according to which a tilting of the plunger due to eccentric forces generates different loads on the parts located in the force flow, which expand or compress or move differently according to Hooke's law as a function of the acting force, must therefore be more deliberately taken into account, amongst others, because complex structural additions can have a disadvantageous impact on the entire system.
The solution described by DE 196 42 587 A1 disadvantageously shows the person skilled in the art that it is only usable in a press that is driven by way of one drive and that the drive is distributed to several pressure points through a power distribution. It is thus not possible to influence the uniform or non-uniform forming process in any way by way of a control or adjustment of the drive.
Apart from these proposed solutions, sliding guides, for example, which are not adjustable or only adjustable along several axes, have been used for compensatory movements in presses. Complex rolling guides (roller bearing guides) are alternately also used, even in an elaborately pre-loaded state.
In order to prevent damage to these technical mechanisms in case of unexpected operating states, very complex protection mechanisms are therefore sometimes installed for preventing overloads.
The invention assumes that all these expenses and devices, such as guide and protection devices, can be dispensed with if the desired parallel movement of the plunger can be provided by controlled and regulated drive motors. In case of malfunctions, it must also be possible to allow a tilting or inclination of the plunger. Until now, solutions to this effect have not been covered by current developments and have been virtually excluded.
At the same time, the problem emerges of initiating a deviation from the desired parallel movement of the plunger, such as a tilting or inclination in a targeted manner, if expedient for the process, and of inducing such positions of the plunger by means of elements of the drives.